FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
Current Consumption
Mode
MODE
EN Pin
SCK/SDA Pins
I2C Bit Command
Comments
Low
High
Low
Low
Low
Low
Low
N/A
Shutdown
Operational
Shutdown
Sleep
Manual
N/A
Low (> 27 ms)
Active
EN bit = X
SM Bus
EN bit = 0
Active
EN bit = 1
Operational
SETI2C bit = 1
CLRI2C bit = 0
EN bit = X
I2C Low Power
(Shutdown)
Part Doesn’t
Wake-up
Low
High
High
X
X
X
SETI2C bit = 1
CLRI2C bit = 0
EN bit = 0
I2C
Sleep
SETI2C bit = 1
CLRI2C bit = 0
EN bit = 1
Operational
Table 4. Operation Current Consumption Modes
BOOST
HARDWARE OVP:
The integrated boost converter operates in non-
The OVP value should be set to greater than the maximum
LED voltage over the whole temperature range. A good
practice is to set it 5.0 V or so above the max LED voltage.
synchronous mode and integrates a 3.0 A FET. An integrated
sense circuit is used to sense the voltage at the LED current
mirror inputs and automatically sets the boost output voltage
(DHC) to the minimum voltage needed to keep all LEDs
biased with the required current. The DHC is designed to
operate under specific pulse width conditions in the LED
drivers. It operates for pulse widths higher than 4.0 μs
If the pulse widths are shorter than specified, the DHC
circuit will not operate and the voltage across the LED drivers
will increase to a value given by the OVP minus the total LED
voltage in the LED string. Therefore it is imperative to select
the proper OVP level to minimize power dissipation.
The boost converter also features internal Over-current
Protection (OCP) and has a user programmable Over-
voltage Protection (OVP).
The OCP operates on a cycle by cycle basis. However, if
the OCP condition remains for more than 10ms then the
device turns off the LED Drivers, the Boost goes to Sleep
mode and the output FAULT pin goes into high-impedance.
The device can only be restarted by recycling the enable or
creating a Power On Reset (POR).
The user can program the boost frequency by I2C
(BST[1:0]) only after the IC is powered up and before the
boost circuit is turned ON for the first time (PWM pin low to
high). This sequence avoids boost frequency to be changed
inadvertently during operation. The first I2C command has to
wait for 5.0 ms after the part is turned ON, in order to allow
sufficient time for the device power up sequence to be
completed.
The OVP can be set from 11 to 62 V, ~4.0 V spaced, using
the I2C interface (OVP Register). If I2C capability is not
present, the OVP can be controlled by a resistor divider
connected from VOUT to GND with its mid point tied to A0/
SEN pin (threshold = 6.5 V). During an OVP condition, the
output voltage will go to the OVP level which is programmed
via the I2C interface or settled by a resistor divider on A0/SEN
pin, or by a zener diode. The formulas to calculate the
hardware OVP using any of the two methods are as follows:
The boost controller has an integral track and hold
amplifier with indefinite hold time capability, to enable
immediate LED on cycles after extended off times. During
extended off times, the external LEDs cool down from their
normal quiescent operating temperature and thereby
experience a forward voltage change, typically an increase in
the forward voltage. This change can be significant for
applications with a large number of series LEDs in a string
operating at high current. If the boost controller did not track
this increased change, the potential on the LED drivers would
saturate for a few cycles once the LED channels are re-
enabled.
Method 1
Method 2
VOUT
R
V
ZENER2
UPPER
A0/SEN
A0/SEN
R
LOWER
OVP = V
+ 6.5 V
ZENER2
OVP = 6.5 V [(R / R
) + 1] + (100E-6 x R )
UPPER
UPPER
LOWER
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
14
FREESCALE [ Freescale ]
